This invention relates to variable resistance devices and, more specifically, to control mechanisms for rapidly and precisely adjusting the resistance level within a circuit.
As known in the art, many electrical circuits require a precise control to vary the voltage and/or current. Consequently, such control is accomplished normally by making fine adjustments to the setting of a variable resistor in such electrical circuits. Typical approaches to the control of a variable resistor utilize multi-turn variable resistor arrangement, since a single turn arrangement often cannot be set with sufficient precision to satisfy the circuit requirements. Such a multi-turn resistor arrangement, however, results in a loss of efficiency and ease of operation, because a significant amount of time is required to turn the shaft the requisite number of several rotations.
Some approaches utilize an external reduction drive connected to the resistor shaft. Such an arrangement requires additional panel space and is relatively expensive to incorporate with respect to the cost of the resistor itself.
Quite often there is the need for dual controls depending upon the requirements of the electronic device. This dualism of function and controls is very common in the electronic service instruments and audio entertainment equipment. Dual controls are found on virtually all types of audio equipment to perform such a function as tone and volume controls as well as left and right loudspeaker balance controls. Further, oscilloscopes and chart recorders typically utilize a pair of variable resistors to adjust the "X" and "Y" axes trace positions. Very often these function controls are accompanied by a linear control providing a finer adjustment of the initial setting.
One approach of manufacturers has been to utilize variable resistors mounted in tandem with coaxial control shafts in order to minimize the amount of panel space required for two variable resistors. However, the utilization of this coaxial control shaft arrangement results in some frequent and annoying problems such as the inadvertent disturbance of the other common axis control when making an adjustment. This difficulty is accentuated by the fact that instrumentation designs strive to achieve a maximum compactness and, therefore, very little panel space is available and controls must frequently be positioned very closely to provide desired features within the allotted space. Consequently, when making precise control movements of the shafts, there is very often a problem of disturbing an adjacent or coaxially mounted control.